Abstract

We propose a polymer photovoltaic device with a new scattering mechanism based on photon absorption and re-emission in a quantum dot layer. A matrix of aluminum nanorods with optimized radius and period are used to modify the coupling of light emitted from the quantum dots into the polymer layer. Our analysis shows that this architecture is capable of increasing the absorption of an ordinary polymer photovoltaic device by 28%.

Figures (10)

Schematic of the polymer cell and simulation procedure. Light is incident from the glass,
and useful absorption during the first path (P1) occurs in both the polymer (P3HT:PCBM) and
within the QD layer. The QDs will emit photons with a particular probability resulting in a
second path (P2) through the cell, which can be absorbed in the polymer.

The (a) real and (b) imaginary parts of the refractive index of the quantum dots used in
our model. (c) Comparison of absorption spectrum of the quantum dots in the model (blue) to
the experimental data (red) shows good agreement.

The number of photons absorbed in (a) the polymer, (b) the QD layer, and (c) the aluminum
nanorods during the first path. (d) The coupling efficiency of the emitted photons from the
QDs to the polymer layer.

Total number of photons absorbed in the polymer for different radii and periods of the
nanorod array (including the absorption from the emission of QDs). The radii are 30 nm
(purple), 50 nm (blue), 70 nm (green), 90 nm (red).

Absorption comparison during the first path for the traditional polymer cell and the QD
enhanced polymer cell. (a) Cross section showing the number of absorbed photons per cubic
meter with (green solid line) and without (blue solid line) the QD layer. (b) The absorption
in each layer of the ordinary polymer cell. (c) The absorption in each layer of our QD
enhanced polymer cell. The absorption in the QDs occurring for λ>600 nm will not
contribute to the re-emission process because they do not contain sufficient energy to cause
emission.

The comparison of absorption spectra of the polymer (blue) and the QD enhanced polymer
(Green: without QD emission, Red: with 50% QD emission, Black: with 100% QD emission) cells
without the nanorod array. (a) The absorbed number of photons as a function of wavelength
under AM 1.5G solar illumination. (b) The percentage of photons absorbed compared to the
incident solar illumination. Note: the peak at ~560 nm results from the absorption of photons
emitted from the QDs and could in principle exceed 100% due to the redistribution of higher
energy photons. The radius and period of the nanorods are 30 nm and 260 nm, respectively.

Electrical field intensity of fundamental (a) TE and (b) TM modes in the solar cell. Orange
and gray lines are the field intensities for structures with and without quantum dots,
respectively. The layers are depicted on the background: glass (blue), ITO (light blue),
polymer (red), QDs (yellow), and aluminum (gray); note: for the structure without QDs, the
yellow layer is aluminum. The analysis is performed at the emission peak of QDs (i.e. 559
nm).

The coupling of dipole emission into the waveguide mode of the solar cell. Blue data are
fundamental (a) TE and (b) TM modes, and red data are the field intensities resulting from
dipole emission. The layers are depicted on the background: glass (blue), ITO (light blue),
polymer (red), QDs (yellow) and aluminum (gray).

The number of absorbed photons is influenced by the thickness of the polymer layer. The
structure with quantum dots outperforms the structure without quantum dots for polymer
thicknesses below 80 nm. For thicker films, there is a tradeoff between carrier collection
and thin-film interference effects.